Secretory immunoglobulins. Using sheep colostrum as the model for exocrine secretions a study is being made of its immunoglobulin composition. Emphasis is given to a study of the presence of J-chains and secretory component in various classes of antibody. Antisera and physicochemical techniques are used for their detection and characterization. Human 13 S Immunoglobulin G and other M proteins. We are examining monoclonal IgG and IgM antibodies from plasma-cytomas. One such material is an IgM cryoglobulin with specific activity against secretory IgA. The nature of this interaction is under investigation. Another IgG myeloma is a 15 S aggregate which may require intact Fc regions for interaction.